Angled flying lead wire bonding process

ABSTRACT

A method is described having the steps of providing a surface having a plurality of wire bondable locations; wire bonding a wire to each of the wire bondable locations using a wire capillary tool; controlling the position of the capillary tool with respect to the substrate; after forming a wire bond of the wire to the wire bondable location moving the capillary tool relative to the surface as the capillary tool is moved away from the surface to form a wire having a predetermined shape.

This application is a Continuation of, application Ser. No. 10/736,890,filed on Dec. 16, 2003, U.S. Pat. No. 7,495,342, which is a Division ofapplication Ser. No. 10/342,167, filed on Jan. 14, 2003, U.S. Pat. No.6,708,403, which is a Continuation of application Ser. No. 09/871,536,filed on May 31, 2001, U.S. Pat. No. 6,526,655, which is a Division ofapplication Ser. No. 09/164,470, filed on Oct. 1, 1998, U.S. Pat. No.6,295,729, which is a Continuation-in-part of application Ser. No.09/088,394, filed on Jun. 1, 1998, U.S. Pat. No. 6,300,780 which ClaimsPriority from Provisional Application No. 60/060,877, filed on Oct. 2,1997, which is a Division of application Ser. No. 08/754,869, filed onNov. 22, 1996, U.S. Pat. No. 5,821,763, which is a continuation ofapplication Ser. No. 08/055,485, filed Apr. 30, 1993, U.S. Pat. No.5,635,846, which is a Continuation-in-part of application Ser. No.07/963,346, filed on Oct. 19, 1992, U.S. Pat. No. 5,371,654.

FIELD OF THE INVENTION

The present invention is directed to a process for bonding wires tosurfaces, for example, to form electronic device probes, or to formelectrical connections on electronic circuit devices and particularly towires that are bonded at one end with the other end free.

BACKGROUND OF THE INVENTION

Wire bonding techniques were first developed back in the 1950's forconnecting germanium transistors to other electronic devices. Wirebonding techniques continue to be used for the vast majority ofintegrated circuit device connections. Thermal energy, mechanical forceand ultrasonic vibrations are used to bond the tiny wires to the deviceterminals.

The Angled Flying Lead (AFL) wire bonding process disclosed herein usesthe same basic processes that are used for a standard thermosonic ballbonding operation and it was developed for fabricating a variety of areaarray and peripheral interconnections including high density land gridarray connectors and high density IC probes.

Conventional wire bonding operation used to make structures according tothe present invention as, schematically shown in FIG. 1, a free end of awire is ball bonded to a contact pad on a surface. The wire is bent overand wedge bonded to another pad. The wire joining the two pads iscurved. The shape of the curve is determined by the distance between thetwo pads which are joined. If the wire joining the two pads are severed,two wires having different shapes are formed. If it is desired that thewires bonded to the surface be used as an electronic device probe (asdescribed herein) or to interconnect an array of contact pads on a firstsurface to another array of contact pads on a second surface which isfacing the first surface, the conventional wire bonding process is notuseful to fabricate such structures. To fabricate a probe for anelectronic device using wires (probe wires) bonded to a surface, one endof the wire is bonded to contact pads on a support substrate for theprobe wires. The other ends of the probe wires must be positioned so asto be able to contact the contact pads on device being tested. When anelectronic device probe is moved into engagement with the contact padsof the device under test, the probe wires preferably flex so that thefree end (probe tip) of the wires wipe across the surface of the contactpad being probed. The wiping action permits the probe tip to make goodelectrical contact to a contact pad. Since a probe is used many times,the probe tips of the probe wires make many thousands (preferablygreater than 1000, more preferably greater than 10,000, most preferablygreater than 100,000) engagements and disengagements with contact padson devices under test resulting in many repeated bendings. The probe tipalso must be flexible enough to achieve the desired degree of wiping,withstand many engagements without deforming and be sufficientlycompressible to without deformation. Applicants invention provides amethod and approach which can reliable form many probe wires to adesired predetermined shape to satisfy all these requirements.

There is a need for a technique to form wires bonded to surfaces wherethe wires can be formed to have any desired shape to provide certaindesired properties. The wires can be bonded to electrical contact padson a surface drawn away from the surface and cut to have a free end. Thewires are bent so that the free ends are placed in a predetermined shapewhich provide advantageous properties, such as a desired flexibility.

SUMMARY OF THE INVENTION

It is the object of the present invention to provide a process forbonding wires to an electronic circuit device with one end of the wireattached to the surface of the device and the other end of the wireextending away from the surface of the device.

Another object of the present invention is to provide a process forbonding wires to an electronic circuit device with the wires formed atan angle to the surface of the device.

A further object of the present invention is to provide a process forbonding wires to an electronic circuit device with the wires havingcurved features.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects, features, and advantages of the presentinvention will become apparent upon further consideration of thefollowing detailed description of the invention when read in conjunctionwith the drawing figures, in which:

FIG. 1 shows the standard wire bonding process steps used to makestructures according to the present invention.

FIGS. 2-6 show the preferred embodiment of the angled flying lead wirebonding process.

FIGS. 7-8 show the alternate embodiments of the angle flying lead wirebonding process.

FIG. 9-12 show various configurations of flying lead wire geometries.

FIG. 13 shows a variety of shapes of the wire tip ends created tofacilitate the engagement of wire tips with electronic device pads.

FIG. 14 schematically shows a frame structure to be used to control thewire position accuracy and, in the mean time, provide matched thermalcoefficient to that of silicon at elevated wafer testing temperatures.

FIG. 15 is a schematic diagram showing the structures according to thepresent invention in testing apparatus.

FIG. 16 is the structure of FIG. 14 with the space between element 153and 11 filled with compliant medium 155.

DETAILED DESCRIPTION OF THE INVENTION

Structures according to the present invention are made using a wirebonding operation is shown in FIG. 1 and starts by forming a ball on theend of a (preferably) gold wire 110 that is threaded through a hollowpointed ceramic tool called a capillary 115. The ball 112 is pressedagainst the first bonding surface 116 of substrate 118 while thesubstrate 118 is heated from below and ultrasonic energy is appliedthrough the capillary 115 as shown in step 1 of FIG. 1. The metallurgyon the surface of the substrate is critical to the wire bonding process.After ball bonding the wire to the first substrate surface 116, thecapillary 115 is raised while the substrate is moved (shown by arrow120) to create a loop shape in the wire (FIG. 1—step 2). The capillary115 is then lowered to press the side 124 of the wire against the secondsubstrate 126 surface 128 to form the second bond or wedge bond 130(FIG. 1—step 3). The capillary is raised slightly indicated by arrow 132and a mechanical clamp is actuated to hold the wire in place while thecapillary is raised again to break the wire at the end of the wedge bond134 (FIG. 1—step 4). The ball is formed on the end of the gold bond wireby placing an electrode below the tip 136 of the wire and using a highvoltage electrical discharge to melt the end of the wire (FIG. 1—step5).

FIG. 2 shows a cross section of an electronic circuit component (11) andseveral angled flying leads (10) attached to the first surface (12) ofthe component (11) according to the present invention. The angled flyingleads (10) can be attached to a variety of different electronic circuitcomponents (11). The angled flying leads (10) are bonded to metallizedcircuit pads (13) on the first surface (12) of the electronic circuitcomponent (11). The electronic circuit component (11) must provide arigid base for the thermosonic wire bonding process to be successful.FIGS. 1, 2, and 3 of the angled flying lead wire bonding process areessentially the same as a standard thermosonic wire bonding process. Anelectrical discharge (22) from an electronic flame off (EFO) unit (21)at surface 20 is used to melt the end of the bond wire (16) extendingthrough the tip of a ceramic capillary tool (15). The electricaldischarge (22) is controlled to provide a consistent sized ball (14) onthe end of the bond wire (16).

FIG. 3 shows the ceramic capillary tool (15) used to press the ballshaped end of the bond wire (16) against the metallized pad (13) on thesurface of the electronic circuit component (11). Ultrasonic energy (30)applied through the ceramic capillary tool (15) and thermal energyapplied through the base holding the electronic circuit component (11)in used to form a ball bond (19) between the bond wire (16) and themetallized pad (13) on the surface of the electronic circuit component(11).

FIG. 4 shows the movement of the electronic circuit component (40) andthe movement of the ceramic capillary tool (41). The movement of theelectronic circuit component (40) is used to define the offset betweenthe free end (18) of the angled flying lead (10) and the ball bond (19)attached to the electronic circuit component (11). The movement of theceramic capillary tool (15) provides sufficient slack in the bond wireto minimize stress to the ball bond (19) during the subsequentoperations.

FIG. 5 shows additional movement of the ceramic capillary tool (50) thatis used to form the angled and curved geometry (17) of the angled flyinglead (10). The movement of the capillary tool (50) must be controlled toprevent deformation of the adjacent angled flying leads (10).

FIG. 6 shows the shear blade (60) that is used to sever the bond wire(62) to form the free end (18) of the angled flying lead (10). The shearblade (60) is precisely located (61) to ensure accurate positioning ofthe free end (18) of the angled flying lead (10). A clamp is used tohold the bond wire while the ceramic capillary tool (15) is raised (62)and the bond wire is severed at the tip of the shear blade (60).

FIG. 7 shows the retraction of the shear blade (70) and the upwardmovement of the ceramic capillary tool (71). The end of the bond wire(72) extending through the tip of the ceramic capillary tool is used forthe next ball bond and the process is repeated to form the desirednumber of angled flying leads (10) on the electronic circuit component(11).

FIG. 8 shows an alternate embodiment of the wire cutting process shownin FIG. 5. The alternate wire cutting process shown in FIG. 7 uses twoshear blades (80, 83) instead of a single blade. The movement andpositioning (81, 84) of the two blades (80, 83) is synchronized to nickthe wire on opposites sides and allow the wire to fracture at thispoint. The double-blade configuration can be used for cutting wires thathave a high tensile strength. The two blade configuration alsosignificantly improves wire positioning accuracy.

FIG. 9 shows a second alternate embodiment of the wire cutting processsimilar to the two blade process shown in FIG. 8. The second alternatewire cutting process shown in FIG. 9 is used for creating straight wires(100) attached to an electronic circuit component (11). The movement andpositioning (91, 94) of the two blades (90, 93) is controlled to nickthe opposite sides of the wire and allow the wire to fracture at thispoint.

FIG. 10 shows three wire configurations (120, 121, 122) attached to anelectronic circuit component (11) using the angled flying lead wirebonding process. All three of the wires (120, 121, 122) are created withthe height (124) from the surface of the electronic circuit component(11). The three wire configurations include a straight wire (120), anangled wire (121), and a wire (122) with a section parallel to thesurface of the electronic circuit component (11). Variations of thesethree wire configurations (120, 121, 122) can be created including wireswith different angles (123) and different wire offset (125) dimensionsas shown on the angled wire (121).

FIG. 11 shows four wire configurations (130, 131, 133, 134) attached toan electronic circuit component (11) using the angled flying lead wirebonding process. The four wire configurations include two straight wires(130, 131) with different wire heights (132, 136) and two angled wires(133, 134) with two different wire heights (135, 137).

FIGS. 12 and 13 schematically show a variety of wire shapes (141, 142,143, 144, 145, 146, 147, 148) practiced by the present invention. Thedifferent wire shapes are created by controlling both the down-movementof the capillary tip and the off-set move of the wire bonding stage. Theshapes continuously curved, piece wire curved, piece wire linear andcombinations thereof.

FIG. 13 schematically shows several shapes and geometries of the wiretip ends, such as straight (167), straight with pointed contact (166),straight with point contact deposited with a suitable contact metallurgy(165), straight end with sharp spikes (164) and deposited with asuitable contact metal (163), ball-shaped (162), ball-shaped depositedwith a suitable contact metallurgy (161) and deposited with sharp spikes(160) at the contact ends.

FIG. 14 schematically shows a frame structure (150, 153) which can betailored to match the thermal expansion coefficient of silicon and othermaterials. The wire tip ends (152) need to be maintained in preciseposition before and after engagement with electronic device pads at upto 180° C. The various contact geometries as shown in the figure arefabricated at the end of wires to facilitate various contact and testapplications.

FIG. 15 is a schematic diagram showing the structures according to thepresent invention in testing apparatus. The testing apparatus 208 has ameans 202 for disposing the probe tip ends 210 on a substrate 200 incontact with contact locations 212 on the device under test 204 which isdisposed on support 206.

The minimum spacing between angled flying leads is dependent on thediameter of the bond wire that is used and the size and geometry of thecapillary tip used for bonding the wires. Smaller diameter wires can bebonded closer together. The capillary tip geometry can be modified usinga bottleneck configuration or a side relief to allow closer bonding ofthe flying leads. The maximum height for an angled flying lead is alsodetermined by the diameter and material properties of the bond wire andthe offset distance between the ball bond and the free end of the wire.Small diameter wires (0.001 to 0.002 inch) are better suited to shorterleads and larger diameter wires (0.002 to 0.003 inch) are better suitedto longer leads. The key material properties of the wire include thestiffness and the tensile strength. The wire properties can becontrolled by the alloys used in the wire material and the elongationfactor used for forming the wire. The structures fabricated according tothe methods of the present invention

The teachings of copending U.S. application Ser. No. 09/088,394 filedJun. 1, 1998 and U.S. Pat. No. 5,371,654 are incorporated herein byreference.

While we have described our preferred embodiments of our invention, itwill be understood that those skilled in the art, both now and in thefuture, may make various improvements and enhancements which fall withinthe scope of the claims which follow. These claims should be construedto maintain the proper protection for the invention first disclosed.

1. A structure comprising flying lead wire structures attached to anelectronic circuit component comprising: said flying lead wirestructures are bonded to a first surface of said electronic circuitcomponent; said wire structures comprise a desired shape in said flyinglead wire; said wire structure not being linear and perpendicular tosaid first surface; and said flying lead wire structures having wire tipends comprising a shear blade cut end.
 2. A structure according to claim1, further including said flying lead wires comprise a plurality ofangles relative to the surface of said electronic circuit component. 3.A structure according to claim 2, said flying lead wires comprise aplurality of heights relative to the surface of said electronic circuitcomponent.
 4. A structure according to claim 3, further including saidflying lead wires comprise a shape selected from the group consisting oflinear, piece wise linear, continuously curved, and combinationsthereof.
 5. A structure comprising flying lead wire structures attachedto an electronic circuit component comprising: said flying lead wirestructures are bonded to a first surface of said electronic circuitcomponent; said flying lead wire structures comprise a desired shape insaid flying lead wire structures; and wire tip ends comprising a smallnick on opposite sides of said wires.
 6. A structure according to claim5, further including said flying lead wires comprise a plurality ofangles relative to the surface of said electronic circuit component. 7.A structure according to claim 6, further including said flying leadwires comprise a plurality of heights relative to the surface of saidelectronic circuit component.
 8. A structure according to any one ofclaims 1 or 5, further including said flying lead wires further comprisedisposed in a predetermined position a sheet of material having aplurality of openings therein through which said flying lead wiresproject.
 9. A structure according to claim 8, further including acompliant frame structure, wherein a compliant frame structure is usedto support said sheet of material.
 10. A structure according to claim 8,wherein said sheet is spaced apart from said first surface of saidelectronic component by a flexible support.
 11. A structure according toclaim 8, wherein said sheet is spaced apart from said surface of theelectronic component by a rigid support, said rigid support serves as astand-off, or hard stop, to limit the degree of movement of said wiretip ends in a direction perpendicular to said surface.
 12. A structureaccording to claim 8, wherein said sheet is spaced apart from said firstsurface of the electronic component by a support with a compositestructure of both a rigid and a compliant layer.
 13. A structureaccording to claim 10, wherein a space between said surface of theelectronic component and said sheet is filled with a compliant medium.14. A structure according to claim 13, wherein said the compliant mediumis an elastomeric material.
 15. A structure according to claim 13,wherein said the compliant medium is a foamed polymer material.
 16. Astructure according to claim 10, wherein said flexible support isselected from the group consisting of a spring and an elastomericmaterial.
 17. A structure according to claim 8, wherein said wire tipends comprise a structure selected from the group consisting of aprotuberance, a spherical contact geometry, a straight contact end, asharp spike, multiple sharp spike, sharp nodules and the combination ofthe above.
 18. A structure according to claim 8, wherein said wire endtips are coated with a material selected from the group consisting ofIr, Pd, Pt, Ni, Au, Rh, Ru, Re, Co, Cu, and their alloys.
 19. Astructure according to claim 8, wherein said angle flying lead wire iscoated with a material selected from the group consisting of Ir, Pd, Pt,Ni, Au, Rh, Ru, Re, Co, Cu, and their alloys.
 20. A structure accordingto claim 8, wherein said sheet comprises materials selected from thegroup consisting of Invar laminate, a Cu/Invar/Cu laminate andmolybdenum laminate.
 21. A structure according to claim 8, wherein saidsheet comprises a material selected from the group consisting of ametal, a polymer, a semiconductor and a dielectric.
 22. A structureaccording to claim 20, wherein said the sheet is over-coated with apolymer layer.
 23. A structure according to claim 20, wherein the sheetis overcoated with an insulating layer.
 24. A structure according toclaim 20, wherein the sheet is overcoated with a thin compliant polymerlayer.
 25. A structure according to claim 20, wherein the sheet islaminated between two insulating layers.
 26. A structure according toclaim 8 further comprising: a means for holding said electronic circuit,means for retractably moving said electronic circuit towards and awayfrom said electronic device so that said wire tip ends contactelectrical contact locations on said electronic device, and means forapplying electrical signals to said elongated electrical conductors. 27.A structure according to claim 1, wherein said electronic circuitcomponent is a substrate having an electrical conductor pattern.
 28. Astructure according to claim 1, wherein said flying lead wire structuresfurther comprise a coating.
 29. A structure according to claim 5,wherein said flying lead wire structures further comprise a coating. 30.A structure according to claim 28, wherein said coating is selected fromthe group consisting of Ir, Pd, Pt, Ni, Au, Rh, Ru, Re, Co, Cu andalloys thereof.
 31. A structure according to claim 29, wherein saidcoating is selected from the group consisting of Ir, Pd, Pt, Ni, Au, Rh,Ru, Re, Co, Cu alloys thereof.